The present invention relates to a phase detector that compares the phases of data and clocks and outputs the result of comparison.
Two types of phase detectors are general phase detectors used for a phase-locked loop (PLL) and a clock-data recovery (CDR) circuit. The first type of general phase detector is a Hogge phase detector. See C. R. Hogge, “A Self Correcting Clock Recovery Circuit”, J. Lightwave Technol., vol. LT-3, pp. 1312-1314, December, 1985. The second type of general phase detector is an Alexander phase detector, also called a bang-bang phase detector. See J. D. H. Alexander, “Clock Recovery from Random Binary Signals”, Electron Lett., vol. 11, no. 22, pp. 541-542, October, 1975. The Hogge phase detector outputs the linear result of a comparison of the phases between data and clocks, based on a difference between the phases of the data and the phases of the clocks. The Alexander phase detector detects only whether the phases of clocks are earlier or later than the phases of data and outputs the binary result.